I was recently reading a book that is newly published by a friend of mine, it's set in the time of Atenism and mostly deals with one of the pharaoh's wives ...
But in the first chapter, she has the MC mention reading the defiled walls of a temple to Bastet in which, according to the partially damaged hieroglyphs where the name of the goddess and her offspring were chipped out, they "offered up the virginity of young girls".

In all my years of passive research, I've never heard of such a thing.

I don't understand what you mean by "offer up the virginity of young girls". This could sound like a pygmy ceremony where the kids who have become of age get together in a festival to be wed. Or it could sound like a human sacrifice which evidence shows has happened only in the first dynasty at Abydos when the kings died, their servants were sacrificed and were buried with their king. There is also a possibility of it having occurred in Naqada, but we do not know for certain.